The Great Quake: 1906-2006 / Bracing for the next 'big one'

As scientists gather, there are grim calculations of the anticipated toll.

Death and damage from the great earthquake and fire of 1906 were terrible indeed, but if that same magnitude 7.9 temblor strikes again along the San Andreas Fault, the toll would be far, far worse, seismic engineers and scientists have calculated.

Consider their chilling forecast for a quake that ruptures the ground for nearly 300 miles, as it did a century ago:

-- At least 3,400 people in a 19-county region from Mendocino to San Benito would die if the quake struck during the day when streets were filled, offices were occupied and children were in school; if it hit at night, -- at, say, 2 a.m. -- the death toll would fall to at least 1,850.

-- From 160,000 to 250,000 people would become refugees and, over time, as many as 300,000 to 400,000 would need to be relocated as the extent of the damage to their homes was revealed.

-- Some 10,000 commercial buildings would be made unusable, while numberless unreinforced homes would be destroyed.

-- It would take more than $150 billion to repair more than 90,000 buildings, restore full service to utilities and transportation systems and overcome widespread economic disruption.

-- A fire similar to 1906's would cause an even more immense loss: as much as $20 billion more in damage, plus uncounted additional deaths.

And when will it happen? The most recent estimates by teams of scientists say the odds are 2 to 1 that a much smaller quake with a magnitude of 6.7 or greater will strike somewhere on one of the Bay Area's seven major seismic faults between now and 2031.

That's 25 years from now, and Mary Lou Zoback, a geophysicist and coordinator of the U.S. Geological Survey's earthquake hazards program, is more definite. She's 53 years old and on Monday she put it simply: "A damaging earthquake will happen here within my lifetime, I'm quite certain," she said. "Truly, there's no safe place to hide here in the Bay Area."

And because the Bay Area is filled with vulnerable buildings, both residential and commercial, there's another warning:

"Five percent of the region's buildings will kill 50 percent of the people who die," said Robert A. Kircher, a Mountain View structural engineer who led the forecasting team.

He and Zoback were among the many scientists and engineers who spoke Monday as they prepared for today's opening of the largest earthquake conference ever held -- a gathering of thousands who are coming to San Francisco the commemorate the 1906 quake centennial and to exchange progress reports on what they've learned about the Earth's erratic behavior over the past century and how best to design buildings to withstand the shock of the Earth's unpredictable future ruptures.

With no safe place to hide, the leaders agreed, the only answer is to prepare for the worst, to retrofit all homes and buildings that are not yet structurally safe and to continue efforts both to understand how and where quakes start and how to minimize their damage.

Although buildings are especially vulnerable to quakes when they are made of rigid concrete and steel or unreinforced masonry or if they are failure-prone wood-frame structures with ground floors weakened by gaping garages or storefronts, only 5 per cent of the region's buildings are especially dangerous, Kirchner said.

"Buildings built after the mid-1970s are generally much safer," he said. "In terms of lives lost, we could cut the cost in half just by getting rid our bad buildings."